1. Field of the Invention
The invention pertains to the field of stereographic or xe2x80x9c3Dxe2x80x9d photography and photogrammetry. More particularly, the invention pertains to a single lens instrument which generates three-dimensional models of an image.
2. Description of Related Art
Stereographic photography is the method of producing images which are apparently three-dimensional by recording separate left- and right-eye images. The viewer reconstructs the 3-D image by viewing the two separate 2-D images simultaneously. Stereographic photography has been known since at least the late 19th century, when stereo viewers were a popular parlor accessory.
Such stereo views have historically been created with two lenses on a single camera, spaced apart by approximately the inter-ocular distance of a human head. The Stereo Realist(trademark) series of 35 mm still cameras, popular in the 1950""s, are an example of this kind of imaging. Left and right views were recorded simultaneously through two lens/shutter sets on alternate frames of the 35-mm film. The later Nimslo(trademark) system used four lenses for essentially the same approach.
Stereo movies appeared in the 1950""s. The images were typically created either using two synchronized cameras, or a two-lens system on a single camera. Similarly, the various Stereo TV systems have typically used two cameras (see Lipton, et al, U.S. Pat. No. 4,583,117) or a single camera with two lenses (Lipton, et al, U.S. Pat. No. 4,523,226).
All of the multiple-camera systems have severe drawbacks, in the added complexity and cost of duplicating the complete camera system and the synchronization of the two separate images (this is especially a problem in film (non-video) applications). In addition, the use of two separate lenses (whether on one camera or two) introduces problems of synchronizing focus and view.
The need for solving this latter problem is real, but not addressed by prior art devices. Simply mounting two cameras side-by-side will allow the taking of the left- and right-eye images, and the cameras can be focused on whatever the subject is (although follow-focus of moving objects is problematic). However, there is more to stereoscopic vision than simply having two eyes. A simple experiment will demonstrate the problem. If one holds up a finger at arms length, and brings it closer and closer to the face, it becomes apparent that your eyes do more than merely focus on the finger as it approaches. You also aim each eye independently; becoming more and more xe2x80x9ccross-eyedxe2x80x9d as the finger nears the face. Without this adaptation, most 3-D films tended to induce discomfort as the apparent image distance to the view changed, since the camera views would not shift as one""s instinct might expect.
In addition, fixed convergence or partially or manually adjustable convergence systems do not address the problem that the overlap of the views must change as the focus and/or focal length of the lens changes. The overlap of the two images should be maximized, especially in systems which digitize the two images and use the information to form a three dimensional picture of the surroundings.
There have been a number of devices aimed at simplifying the stereographic process by allowing use of a single camera to take the two images. Most of these use a number of mirrors or prisms, either in front of the camera lens or between a secondary lens and a pair of primary lenses.
One method, useful only with motion pictures, is to sequentially record the two images on alternate frames of the film or video. For film, a synchronized spinning mirror is used to select the view to be recorded in synch with the film gate or video scan. For such a device, see Latulippe, U.S. Pat. No. 3,254,933. In video, the system electronically selects alternate frames from two sources. This method has several disadvantages, requiring complicated synchronized glasses for viewing and being applicable only to movie or video applications.
The other alternative is to record both images simultaneously on each frame, side-by-side or one above the other. This method is applicable to any form of photography, still or moving, silver image or video. Viewing is simplified, since both images are always present, and the adapter to use a single lens does not need to be synchronized to the film transport or video scan.
Simple prism- or mirror-based stereographic adapters have been available for still cameras for some time. They fit in front of the camera lens in the same manner as an accessory close-up or telephoto adapter. They have no means for adjusting the adapter for convergence or focus as the subject-lens distance changes.
Marks, et al, U.S. Pat. No. 4,178,090, creates vertically displaced left and right images on a single frame using an attachment in front of a single lens. One image is straight-through, with the second being taken through a pair of prisms. An adjustable block in front of the lens is solid glass on the top and reflective on the bottom. Convergence is adjusted as the lens is focused by mechanically coupling a rotation control for the adjustable block and a worm gear rotating the lens focus control. This adjustment is insufficient for true automatic convergence control with focus, as only one of the two views changes angle as the block is rotated.
Bukowski (Optimax III, Inc.) U.S. Pat. No. 4,436,369, shows a mirror-based adapter using two primary lenses with ganged focusing mechanisms. Two pairs of fixed mirrors direct the left and right images to the top and bottom of the film frame. The optical axes of the lenses are parallel and fixed, which means that the convergence or aim point of the two lenses is not changed as the lenses are focused.
Fazekas (Panavision, Inc.) U.S. Pat. No. 4,525,045, also has two primary lenses and two pairs of fixed mirrors/prisms. A xe2x80x9chorizon adjustmentxe2x80x9d is provided to allow the cameraman to move one lens to compensate for the vertical displacement of the two lenses, but the optical axes of the lenses are fixed and parallel.
Rockstead, U.S. Pat. No. 4,568,970, uses an adapter which fits in front of the lens of a television camera. Pairs of mirrors or prisms are used to create the pair of images on the video frame, and a similar device in front of the viewer""s eyes reconstructs the two images back into a 3-D single image. A knob allows the operator to manually adjust the convergence of optical axes of the mirrors/prisms to create the two side-by-side images.
U.S. Patent Nos. 5,532,777, 5,828,913, and 5,883,662 by the present inventor disclose a device and method of for generating a pair of images of a subject, left and right, in which the overlap of the images is maximized by adjusting the convergence of the image-collecting means in response to the distance from the subject. An adapter having a set of four mirrors in two pairs is located in front of a camera lens. The centers of the four mirrors are all aligned on a common centerline, with the outer two mirrors facing generally outward along the optical axis of the lens and the inner two mirrors facing generally inward into the lens. The centers of the outer two mirrors are spaced apart by an appropriate interocular distance. The two inside mirrors are together large enough to cover the complete viewing area of the lens, each taking half of the lens viewing area. The two outside mirrors are bigger than the inside pair and large enough to cover the viewing area of the inside pair to avoid viewing area reduction. The convergence of the two outer mirrors is adjustable by swiveling them simultaneously and equally about their centerlines with a ganging mechanism. The two center mirrors may be fixed, or could be adjustable by being swiveled so that one side of each remains in tight contact with the other along the optical axis of the camera lens, and each makes a 45xc2x0 or lesser angle to the optical axis.
An apparatus for creating three-dimensional images is disclosed. The device has at least four mirrors, arranged in an inner set and an outer set. An enclosure, preferably cylindrical in shape, houses the mirrors and alignment apparatus and can be placed in three different positions. The camera takes two-dimensional photographs or operates in two modes of three-dimensional photography: forward looking and backward looking. This device is preferably attached to a digital camera. The device can also be used when the digital camera is attached to a hand held personal computing device (PDA). In a preferred embodiment of the invention, there are six mirrors, including four inner mirrors and one set of outer mirrors.